8 PM Update...the Huskies DID win and will be going to a bowl game!
You think of eastern Washington and what are the first thoughts that come into your head? Dry--no doubt. Sunny and warm? Well for the warmer half of the year this is true...but eastern Washington has its dark side...the tendency for low clouds and fog to collect there from November into February.
The last few days have been good examples. Below are two satellite images from yesterday (Friday, Dec 3). The first from the usual NWS operational satellite and second from the high-resolution MODIS satellite.
Eastern Washington is full of low clouds and fog...and you can see a line of low clouds in the Willamette Valley (also a foggy place), the Chehalis Valley and portions of the Puget Sound basin. In the latter the fog tends to burn off to a much greater degree than eastern Washington.
Foggy conditions tend to occur when high pressure is over our region--bringing light winds and relatively cloud-free conditions aloft. In such situations the earth can effectively radiate heat to space, cooling the surface down to the dewpoint...thus the clouds and fog. Mixing from wind helps to dissipate the low clouds...and this is where eastern WA has a big problem...it is in a topographic bowl. Here's the proof from a google topographic map:
Eastern Wa is surrounded by the Cascades to the west, the Okanogan Highlands to the north, the Rockies to the east, and the Blue Mts to the southeast, with higher terrain north of the Columbia River finishing the enclosure. So on these cold, high- pressure days the cold air collects and deepens in the basin, with a stable inversion capping the cool layer. The clouds are good at emitting infrared to space and maintaining themselves. The result--one gloomy situation.
In Spokane, the number of overcast days per month for November, December, January are 17, 21, and 10, with the corresponding number of heavy fog days (1/4 mile visibility or less) being 8.5, 11.7 and 9.3. You will need vitamin D there for sure.
But wait! There is something else--freezing fog. Since there is often subfreezing temps while this fog is around, the roads are often glazed by dangerous freezing fog. In fact, the National Weather Service has had a freezing fog warning out for several days now.
Fortunately, there appears to be a break in the fog over Pullman for the Apple Cup game...an intervention by higher powers that is a sure sign that the UW Huskies will win. However, if my ability to forecast the weather is admittedly uncertain and my bias in this matter self-evident, I suspect my skill in predicting football scores may be questionable.